Within the field of wireless telecommunications systems there exists a system referred to as the digital enhanced cordless telecommunications (DECT) system. Within the DECT system, a user of a cordless portable telephone handset is able to communicate with a user of another telecommunication device by way of a fixed base station utilizing wireless communication. To enable the cordless telephone handset and the base station to communicate within the DECT system, a radio interface is utilized.
Within the radio interface of the DECT system, there are two communication channels utilized during communication between a cordless telephone and a base station. One of the channels is commonly referred to as the slow C-plane and is used for transmitting control data at a maximum rate of 2 kilobits per second (kBit/s). This control data enable the communication devices to remain synchronized, among other things. The other channel is typically referred to as the U-plane and is used for transmitting user data, which can include either voice data produced by a user of a cordless telephone or digital data generated, for example, by a modem of a computer system. The voice data is transmitted through the U-plane at a rate of 32 kBit/s while the digital data is transmitted through at a rate of up to 80 kBit/s. It should be appreciated that the user data (U-plane data) and the control data (slow C-plane data) can be concurrently transmitted between a base station and a cordless telephone within the DECT system.
There are some situations (e.g., during the initial setup of a call) where the need arises to transfer control data at a faster data rate than is possible through the slow C-plane. As such, the DECT standard additionally defines a fast C-plane transmission mode which enables the transmission of control data at a data rate of either 25.6 kBit/s or 64 kBit/s. The fast C-plane transmission mode, as defined by the DECT standard, involves the U-plane and fast C-plane sharing the same field within the communication frames of the system. As such, during transmission of control data through the fast C-plane, user data cannot be transmitted through the U-plane. In other words, fast C-plane data and U-plane data cannot be transmitted concurrently. A typical prior art circuit for implementing and controlling the transmission of fast C-plane data and U-plane data is discussed below with reference to FIG. 1.
FIG. 1 is a block diagram of a prior art switching circuit 100 conventionally used within a cordless telephone of the DECT system for transmission of user data 102 through the U-plane and of control data 104 through the fast C-plane. As described above, user data (U-plane data) 102 and control data (fast C-plane data) 104 are not simultaneously transmitted. As such, switching circuit 100 is implemented to transmit either user data 102 or control data 104. Furthermore, switching circuit 100 is implemented to grant transmission priority to control data 104. For instance, when switching circuit 100 is transmitting user data 102 and it receives control data 104, the transmission of user data 102 is suspended in order to begin transmission of control data 104. Additionally, the transmission of user data 102 remains suspended until the transmission of the control data 104 is completed. The detailed manner in which switching circuit 100 operates is described below.
Switching circuit 100 of FIG. 1 is able to receive both user data 102 and control data 104. The received user data 102 are stored within a U-plane first-in first-out (FIFO) buffer memory 106, while the received control data 104 are stored within a C-plane FIFO buffer memory 108. An E/U-multiplexer (Mux) 112, as defined within the DECT standard, receives both the user data 102 output from U-plane buffer 106 and the control data 104 output from C-plane buffer 108. It should be appreciated that the function of E/U-Mux 112 is to transfer either the user data 102 or the control data 104 into a DECT channel buffer 114. C-plane buffer 108 controls the operation of E/U-Mux 112 by asserting or de-asserting a signal 110. For instance, upon receiving control data 104, C-plane buffer 108 asserts signal 110, causing E/U-Mux 112 to transfer control data 104 into DECT channel buffer 114. Conversely, if there are no control data 104 within C-plane buffer 108, it de-asserts signal 110, causing E/U-Mux 112 to transfer user data 102 into DECT channel buffer 114. In this manner, transmission priority is granted to control data 104.
The function of DECT channel buffer 114 of FIG. 1 is to encode whichever it receives of the user data 102 or the control data 104 to be transmitted in a time division multiple access (TDMA) format. Then DECT channel buffer 114 either outputs user data 102 through the U-plane as an air channel data stream 116. Or DECT channel buffer 114 outputs control data 104 in the fast C-plane transmission mode as an air channel data stream 116.
There is a disadvantage associated with the prior art fast C-plane transmission mode described above with reference to switching circuit 100 of FIG. 1. The disadvantage occurs during voice connections wherein the fast C-plane transmission mode noticeably degrades the quality of the voice signals of a user of a cordless telephone within the DECT system. This degradation in voice signal quality is caused by the suspension of the transmission of U-plane voice data in order to transmit fast C-plane data. Consequently, this results in a gap within the voice signal data stream.
Thus, what is desired is a system which enables the fast C-plane transmission mode to be utilized during cordless telephone voice connections within the DECT system without degrading or disturbing the quality of the voice signals. The present invention provides this advantage.